In many types of communication systems, such as wireless systems and systems configured based upon radiotelephone-like technology (such as some of the proposed cable systems), sporadic interference may occur.
In cable distributions systems, the system is sealed to prevent the radio frequency (RF) signals from leaking out into the surrounding areas as well as prevent leakage "ingress" into the cable system. This type of ingress can be due to typical wireless systems (e.g. dispatch, cellular, etc.) as well as other types of equipment (e.g. radiation from commercial, medical, and industrial equipment).
When ingress occurs in the downstream spectrum of the cable (the portion currently used for video transmissions) it may be seen as distortion (such as snow) on the picture or effect the sound. The upstream and downstream portions will both be carrying other signals such as voice and data, which may also be corrupted.
Presently, it is expected that ingress is likely to be narrow band in nature (on the order of tens of kilohertz, kHz) and located more in the upstream portion of the cable spectrum. In addition, ingress will be more disruptive to a cable exchange services which provide for alternate, competitive, basic telephony services in local exchange areas or for alternate access to inter-exchange services. The cable exchange service may also provide other special services such as data, ISDN, digital video phone, and interactive multi-media services.
Therefore, it would be desirable for the operators of such a system to minimize the potential distortion and provide a system having optimal performance.